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Abstract

Introduction: Fetal long QT syndrome (fLQTS) has been successfully diagnosed with magnetocardiography (MCG), but there is limited data comparing MCG findings to other clinical manifestations of fLQTS. We hypothesized that severity of rhythm phenotype would be predicted by extent of QTc prolongation.

Methods: We reviewed the fMCG and medical records of fetuses referred to 2 different Biomagnetism Laboratories between 1990 and 2009 in whom a diagnosis of LQTS had been made. From signal-averaged rhythm tracings collected, we calculated fetal heart rate (FHR), QT interval, and using Bazette’s formula, QTc interval. Indication for fMCG was

Family history (FH) of LQTS or

Fetal bradycardia.

We compared fetal (f)-QTc and FHR by ANOVA to published normal data and f-QTc with neonatal (n)-QTc by nonparametric testing.

Results: The cohort consisted of 13 fetuses: 7 referred with a positive FH of LQTS (29.1 ± 7.4 weeks) and 6 referred for bradycardia (27.9 ± 4.0 weeks). The QTc ranged from 453 to 690 ms. All 13 fetuses had bradycardia (FHR < 5th %). Fetus with QTc ≥ 580 ms also had 2° AV block (2 fetuses), torsade de pointes (TdP) (2 fetuses) and/or T-wave alternans (2 fetuses), which persisted after birth. In one additional neonate with f-QTc ≥ 580 ms, 2° AV block and TdP were observed. Two of the three infants with TdP developed ventricular fibrillation. In the cohort, f-QTc was not significantly different from n-QTc.

Conclusion: The f-QTc determined by fMCG predicts the severity of symptoms in fLQTS; f-QTc of > 580 ms increases the likelihood of either fetal or neonatal 2° AV block and/or TdP. We speculate that fMCG findings may risk-stratify the care of infants with LQTS.